Seinen Fan
Technically, seinen refers to any manga/anime aimed at young adult males, but it's fandom has been given a much more precise meaning. Among the larger society of anime fans, Seinen refers mostly to it's sub-genres of Bishoujo, Harem, and Ecchi.

Because of this, Seinen Fans are generally taken to be most interested in the fanservice aspects of an anime, most notably in the form of Zettai Ryouiki, Moe, and panty shots. This has some rather unfortunate implications, as those who do not know the genre will assume that all seinen is hentai, and thus all seinen fans perverts.

Whilst it is true that all Hentai except Yaoi is generally seinen in nature, the vast majority of seinen is non-sexual, and most Seinen fans will never watch a series just for it being hentai, although they will laugh at Ecchi jokes and are more attracted to 'Moe' girls than most anime fans.

Some seinen series include Ah! my goddess, Chobits, and Love Hina. A magazine that typically serializes Seinen manga is Young Jump.

Seinen Fans will typically dress normally, but with t-shirts referring to seinen anime, ocaisionally with somewhat risque imges of moekkos on them, and will listen to music from Seinen anime.